An integrated circuit (IC) that includes two or more dies within a single package is referred to as a “multi-die IC.” One type of multi-die IC, referred to as a “stacked die IC,” is formed by stacking multiple dies. In some cases, a stacked die IC is formed by stacking two or more dies on a surface of another die called an “interposer.” The interposer may provide signal lines, e.g., wires, communicatively linking the various dies attached, or stacked, on the surface of the interposer.
During manufacture, a stacked die IC is susceptible to warpage and, more particularly, warpage of the interposer. Warpage of the interposer may cause defects in the stacked die IC such as inconsistent interconnect formation between interposer and the dies attached thereto and/or between the interposer and a substrate. Warpage may be caused by a variety of different factors. Exemplary factors include, but are not limited to, thickness of the interposer die, processing temperatures, e.g., during solder reflow, differences in coefficient of thermal expansion (CTE) between the interposer die, other dies, and/or substrate, and variance in the thickness of layers of the multi-die IC such as layers of the dies and/or layers of the packaging materials.
Some varieties of stacked die ICs are homogeneous. Homogeneous stacked die ICs generally have a uniform distribution of functional dies attached to the surface of the interposer. In a homogeneous stacked die IC, the surface of the interposer to which other dies are attached does not include regions of any significant size that are unoccupied by attached, functional dies. As a result, homogeneous stacked die ICs exhibit uniform warpage behavior during manufacture that does not lead to an unacceptable number of defects.
Other varieties of stacked die ICs are heterogeneous. Heterogeneous stacked die ICs generally have a non-uniform distribution of functional dies attached to the surface of the interposer. In a heterogeneous stacked die IC, the surface of the interposer die to which other dies are attached does include one or more regions that are unoccupied by attached, functional dies. Typically, these unoccupied regions result from the use of multiple dies of differing size. Heterogeneous stacked die ICs exhibit non-uniform warpage behavior that does lead to an unacceptable number of defects if the non-uniform distribution of dies is not addressed during manufacture.